1. Field of the Invention
The present invention relates to a humidifying module provided with a housing having a bundle of water permeable hollow fiber membranes installed therein. More specifically, the present invention relates to a humidifying module having an inner flow passage through which a fluid passes.
2. Prior Art
The humidifier 100 disclosed in Japanese unexamined patent publication H07-71795 is an example of a humidifier which uses a conventional water permeable hollow fiber membrane. As shown in FIG. 9, the humidifier 100 has a housing 101 with a cylindrical shape that is provided with an inlet 102 and an outlet 103 for loading and discharging dry air provided therethrough, respectively. A hollow fiber membrane bundle 104 includes a plurality of hollow fiber membranes, for example only, 5000, and is installed within the housing 101.
Fixing parts 105 and 105xe2x80x2, respectively, are provided at both ends of the housing 101 to support the ends of the hollow fiber membrane bundle 104 without closing the hollow passages within the fiber membranes. The fixing parts 105 and 105xe2x80x2 are capped with a head cover 108 and 109, respectively. An inlet 106 for loading humid air therein is formed on the head cover 108. An outlet 107 for discharging the humid air, from which moisture contained therein is separated and eliminated, is formed on the head cover 109.
Humid air loaded through the inlet 106 is passed through the inside of each hollow fiber membrane of the hollow fiber membrane bundle 104. At this time, moisture within the humid air is separated by a capillary condensation phenomenon, and the moisture is then moved to the outer surface of each hollow fiber membrane via capillary action. The humid air from which the moisture is separated is then discharged through the outlet 107.
Dry air (i.e., a low humid gas) is loaded through an inlet 102 and passes through the outer surface of each hollow fiber membrane of the hollow fiber membrane bundle 104. As a result, the dry air is humidified by the moisture separated from the humid air described above. The humidified dry air is then discharged through the outlet 103.
Another humidifier 200, as shown in FIG.10, is known as xe2x80x9can inner pipe typexe2x80x9d. The humidifier 200 includes a plumbing 206 having a barrier which serves as an inner flow passage for loading the humid air into the hollow fiber membranes bundle 204. The plumbing 206 is inserted into the hollow fiber membrane bundle 204 and along a longitudinal axis of the hollow fiber membrane bundle 204.
The hollow fiber membrane bundle 204, which includes a plurality of individual hollow fiber membranes, for example only, 6000, is installed within a housing 201. Fixing parts 205 and 205xe2x80x2, respectively, are provided at both ends of the housing 201 to support the ends of the hollow fiber membrane bundle 204 without closing the hollow passages within the fiber membranes.
Head covers 208 and 209 are provided on the fixing parts 205 and 205xe2x80x2, respectively. An inlet 202 for loading dry air therein is formed on the head cover 209. An outlet 203 for discharging dry air therefrom is formed on the head cover 208.
The plumbing 206, which loads humid air into the hollow fiber membrane bundle 204 by passing the humid air through the through holes 206out, penetrates the head cover 208.
The plumbing 206 passes through both the head cover 208 and the fixing part 205 from the outside, and a tip of the plumbing extends to be within the hollow fiber membrane bundle 204. A total length measured from an inlet 206a to an outlet 206out of the plumbing 206 is established to be shorter than the total length, taken in a direction along the longitudinal axis of the hollow fiber membrane.
An outlet 207 for discharging the humid air, from which moisture contained therein is separated and eliminated by the hollow fiber membrane bundle 204, is formed on the housing 201 next to the head cover 209.
Humid air reaches the through holes 206out by passing through the interior of the plumbing 206 via the inlet 206a. The humid air then streams along the exterior surface of each hollow fiber membrane of the hollow fiber membrane bundle 204.
At that time, moisture within the humid air is separated by a capillary condensation phenomenon, and the moisture then passes through the outer surface and into the hollow fiber membrane. The humid air is then discharged via the outlet 207.
Dry air (i.e., a low humid gas) is loaded through the inlet 202, and passes through the interior of each hollow fiber membrane of the hollow fiber membrane bundle 204. As a result, the dry air is humidified by the moisture separated from the humid air. The dry air is then discharged through the outlet 203.
When the above described conventional humidifier 200 is used in a fuel cell to humidify anode and cathode gasses, several drawbacks must be dealt with. Several of the drawbacks are due to the differences in the shape of a barrier bf at the bottom part 206b of the plumbing 206 or the location of the bottom part 206b. 
Since the exhaust gas (i.e., off-gas) is discharged from a fuel cell containing steam and condensed water, the following drawbacks have been known to occur.
For example, if there is condensed water remaining at the end portion 206b of the plumbing 206 and the water freezes therein due to a low temperature, the plumbing 206 tends to fracture because of the stress caused by volume expansion at the time of freezing.
Additionally, when there is an excessive change of power output from the fuel cell, the time required for attaining the required humidification levels takes too long due to the remaining water at the end portion 206b of the plumbing 206 or because of the time lag for loading the steam into the hollow fiber membrane bundle 204. As a result, operational efficiency greatly decreases.
Moreover, if the water remaining at the end portion 206b of the plumbing 206 is cooled during a period of non-use, such as night term, of the fuel cell, the humidification performance at startup of the humidifier 200 greatly decreases because the high humid gas discharged from the fuel cell is cooled by the cold remaining water. Thus, output or startup efficiency of the fuel cell greatly decreases.
An object of the present invention is to overcome the above-described drawbacks in the industry by providing a humidifying module having a water permeable hollow fiber membrane, wherein an inner flow passage having an end wall is inserted along a longitudinal axis thereof. More particularly, the present invention provides a humidifying module which has improved output and startup efficiency, and prevents water from remaining therein, even if a fluid with steam and condensed water reaches the inner flow passage.
The humidifying module includes a plurality of hollow fiber membranes grouped together to form a hollow fiber membrane bundle, wherein a moisture exchange is performed across a thickness of each hollow fiber membrane between fluid streaming within an interior of each hollow fiber membrane and along an exterior of each hollow fiber membrane. An inner flow passage is inserted within the hollow fiber membrane bundle and along a longitudinal axis of the hollow fiber membrane bundle. A total longitudinal length into which the inner flow passage is inserted within the hollow fiber membrane bundle is shorter than a longitudinal length of the hollow fiber membrane bundle. The inner flow passage includes an inlet and an outlet through which the fluid passes, and an end wall located near the outlet. A protrusion is disposed at the end wall and is opposite to the flow direction of the fluid streaming within the inner flow passage. The present invention provides several advantages.
For example, in the inner flow passage, the inner cross-sectional area gradually decreases in a direction from a tip of the protrusion toward the end wall. Thus, the flow rate of the fluid increases as the fluid flow approaches the end wall.
Additionally, in the inner flow passage, the collision area with the fluid gradually widens as it approaches the end wall. Therefore, the fluid receives shear force along the surface of the protrusion as the end wall approaches, and is pushed radially outward. That is, fluid is pushed outward toward the outer surface more certainly than the inner flow passage of conventional construction wherein the end portion of the inner flow passage is plane shaped and the fluid was received by the entire end portion (i.e., plane surface).
Moreover, in the inner flow passage, as a result of a multiplier effect of these factors, the fluid smoothly passes through the outlet even if steam and condensed water, which tend to easily remain therein, are contained in the fluid.
Also, according to the present invention, the occurrence of any fluid remaining in the humidifying module can be prevented. The drawbacks associated with the conventional modules, such as the fracture of the inner flow passage caused by the remaining water freezing, and the cooling of high-temperature gas discharged from a fuel cell by the remaining water, are prevented. Therefore, the humidifying module, according to the present invention, which provides efficient output and startup to the fuel cell, even if the module is used to humidify gas supplied to the fuel cell, is obtained.
Preferably, the inner flow passage is formed to have a cylinder shape, and the protrusion is formed to have a circular cone shape.
Furthermore, since the same circular members are used, that is, the shape of the inner flow passage is a circular cylinder hollow shape and the shape of the protrusion is a circular cone. Thus, the humidifying module with superior workability is obtained. Since the fluid is supplied over the entire hollow fiber membrane bundle with sufficient fluid distribution in a radial direction, the usability of the hollow fiber membrane is improved.
Additionally, the outlet is a plurality of through holes bored in the circumferential wall of the inner flow passage near the end wall, and at least one through hole is positioned between a tip of the protrusion and the end wall.
According to the present invention, the flow rate to the perpendicular direction of the fluid, in other wards, the rate of diffusion in the radial direction, is increased as a result of arranging the through holes near the end wall of the inner flow passage. Thus, the fluid is supplied over the whole hollow fiber membrane bundle with sufficient fluid distribution toward the radius direction, and the usability of the hollow fiber membrane is improved.
In the present invention, at least one through hole is positioned between the tip of the protrusion and the end wall. In the inner flow passage, therefore, the inner cross-sectional area of the inner flow passage gradually decreases in the direction taken from an inlet toward the end wall. Thus, the fluid flow rate increases as it approaches the end wall.
In the inner flow passage, therefore, the protrusion is provided at the end wall of the inner flow passage so that the tip of the protrusion is opposite to the flow direction of the fluid streaming therein. Thus, the collision area with fluid gradually widens as it approaches the end wall. Therefore, the fluid receives shear force along the surface of the protrusion as it approaches the end wall, and is pushed toward the outside. That is, fluid is pushed toward the outside more certainly than the inner flow passage of conventional construction wherein the end portion of the plumbing is plane shaped and the fluid was received by the entire end portion (i.e., the plane surface).
In the inner flow passage, as a result of the multiplier effect of these factors, when fluid is loaded or directed to the inner flow passage, the fluid directed therein smoothly passes through the outlet because at least one outlet is positioned between the tip of the protrusion and the end wall.
If the outlet is positioned upstream of the tip of the protrusion, since the passing of the fluid is disturbed by the fluid rebounding from the bottom, desirable and effective results are not obtained.